1. Field of the Invention
The subject invention relates to fluorescent tube lighting fixtures for installation in vehicles having direct current electrical systems.
2. Description of the Prior Art
Florescent lighting fixtures including fluorescent light tubes are commonly mounted within the cabins of recreational vehicles, tractor trailers, and small marine vessels to illuminate the interiors thereof. Because these fixtures may be operated when the vehicle's engine is not running, fluorescent lighting fixtures, rather that incandescent lighting fixtures, are desirable due to their relatively low power consumption that minimizes drain on the vehicle's battery.
Fluorescent lighting fixtures typically incorporate circuit board devices having electrical components including single or multiple power transistors mounted on a printed circuit board. Because most recreational vehicles have direct current (DC) electrical systems, the lighting fixture must be configured for use with DC power. The electrical components receive electrical power from the DC power source and convert such DC signal to an oscillating output signal. The output signal is oscillated at a selected frequency for energizing the fluorescent light tube of the fixture. A ballast circuit is also provided which serves to regulate and limit current through the fluorescent tube.
In single power transistor applications, the output signal from the transistor may provide a square wave form that inherently includes a level of harmonic distortion or noise. When such a transistor is incorporated in a lighting fixture mounted within a recreational vehicle and connected to the DC electrical system thereof, such noise may undesirably interfere with other electrical accessories in the vehicle such as the AM radio, citizen's band radio, or the radio navigation system of marine vessels.
To eliminate or to lower the amount of noise distortion to at least acceptable levels, a second transistor may be included in the electronics of the lighting fixture and configured in combination with the first transistor to provide a "push-pull" circuit. The "push-pull" circuit provides an output sine wave signal that provides much less noise distortion. Thus, a lighting fixture having the "push pull" circuit may be selected for certain low noise distortion applications. Furthermore, the additional second transistor may provide greater power output for use with higher wattage fluorescent light tubes and or multiple tube fixtures. Although these low distortion fixtures are more expensive, consumers desire to purchase the lower noise distortion lighting fixtures to eliminate interference with other vehicle accessories.
In the factory setting, preassembled circuit board devices are separately manufactured to provide the particular electrical power configuration, be it a single transistor or a double "push-pull" transistor configuration for subsequent mounting within the housings of particular lighting fixtures. The circuit board devices are typically of a standard size configured for common mounting orientations within the fixture housings to facilitate high volume assembly.
Inherently, power transistors generate a large amount of heat, and thus are typically integrally housed in a heat sink or heat dissipative package. In some devices, the transistor package may be itself configured to fixedly mount the circuit board to the fixture housing. This is accomplished by molding the transistor package in the form of a mounting foot. In the single transistor configuration, a single transistor mounting foot may be mounted to the circuit board to project outwardly therefrom. The mounting foot may be provided with a mounting bore for alignment with a mounting hole in the fixture housing such that a rivet may be fastened therethrough. As such, the rivet engages the mounting foot to secure the mounting foot directly to the fixture housing. In such a configuration, heat is transferred through the mounting foot to the fixture housing to more effectively dissipate heat generated from the transistor.
The "push-pull" type circuit board devices may include a pair of identical mounting feet, each mounting foot integrally formed with a transistor therein. The pair of transistor mounting feet may be disposed at one end of the circuit board in a predetermined laterally spaced apart configuration. Thus, a second fixture housing may have to be provided formed with two spaced apart mounting holes therethrough for receiving a pair of fastening rivets to secure the respective mounting feet to the fixture housing.
In the production environment, lighting manufacturers typically manufacture a multitude of fluorescent lighting fixture housings of different styles having different widths and lengths to house a variety of different size fluorescent light tubes. Furthermore, the fixture housings may be configured to house one or a multitude of fluorescent light tubes. As such, many lighting fixture manufacturers may have upwards of a hundred or more different types of fixture housings in inventory.
Lighting manufacturers typically have high-volume automated tooling fixtures and jigs set-up in the factory to manufacture such a variety of fixture housings and lighting fixtures. However, such equipment may only be set-up to produce fixture housings having a mounting configuration for either the single power transistor-type circuit board or the "push-pull" -type circuit board. For instance, the production line may be set up with fixturing for mounting a circuit board device having only the single transistor configuration. To procure additional equipment and re-tool the factory to supply a second fixture housing for mounting the alternative "push-pull" circuit board device, the manufacturer may expend many thousands of dollars. In addition, many days or weeks of downtime may be incurred in retrofitting the existing equipment with the necessary fixtures to manufacture a second series of fixture housings. Furthermore, providing a second series of fixture housings increases manufacturing costs and doubles inventory.
Therefore, it is desirable to provide a fluorescent tube lighting fixture wherein at least two differently configured pre-assembled circuit boards including either one or two integrally formed transistor mounting feet may be mounted to a single common fixture housing. As such, tooling time and manufacturing expenses necessary to fabricate two differently configured fixture housings may be eliminated. In addition, inventory and the expenses associated therewith are minimized.